The present invention relates to a power supply, and more particularly to a power supply incorporating power factor correction.
Electric power is distributed almost universally in an alternating current (AC) format that allows for efficient transmission. Most devices however, including personal computers, televisions, etc., require direct current (DC) power. Power supplies act to convert the AC input supplied by a line to a DC output suitable for consumption by a device or load. A switched-mode power supply (SMPS) employing a boost regulator is commonly employed in this role of AC-to-DC power conversion. A benefit of employing a SMPS having a boost regulator topology is the boost regulator can be controlled to provide power factor correction.
The term ‘power factor’ refers to the ratio of real power to apparent power, wherein real power represents the power available to do work within the circuit and apparent power is the product of the current and voltage provided to the circuit. A power factor of ‘one’ indicates that all apparent power is converted to real power. The power factor is decreased by factors such as phase differences between the input current and voltage as well as non-linearities associated with either the input current or voltage. For example, switched-mode power supplies draw a non-sinusoidal current that decreases the power factor of the device.
To improve the power factor associated with power supplies, such as switched-mode power supplies, a power factor correction (PFC) controller incorporates a current control loop that is based on inputs that typically include the AC input current drawn by the power supply, the AC input voltage provided to the power supply, and the DC output voltage of the power supply, drives the input current to a sinusoidal shape that tracks the AC input voltage, and controls the DC output to a desired value. A number of control loops are well-known in the art for providing active power factor correction to switched-mode power supplies (e.g., continuous current mode controllers, transition mode controllers, etc.). However, many of the problems encountered by active power factor correction controllers are related to how the controller handles fault conditions associated with the switched-mode power supply.